The invention relates to a spring-loaded mechanical control mechanism for a circuit-breaker in a high-voltage or medium-voltage grid, said control mechanism comprising a toothed wheel turned by a spring from a first angular position to a second angular position, and a cog wheel co-operating with the toothed wheel to displace it from the second angular position to the first angular position so as to tension said spring, said toothed wheel having a peripheral set of teeth constituted firstly by a primary set of teeth secured to the wheel, and secondly by a portion of a set of teeth in the form of a retractable toothed segment, said primary set of teeth having a constant pitch.
A xe2x80x9ccircuit-breaker in a high-voltage or medium-voltage gridxe2x80x9d is to be understood as covering any interrupting switchgear designed for an electricity grid whose operating voltage is greater than 1 kV.
The invention may firstly be applied to a mechanical control mechanism in which the toothed wheel is secured to a single control shaft coupled to a moving contact of the circuit-breaker in order to close the circuit-breaker by the engagement spring relaxing, the spring thereby driving the wheel. The invention may also be applied to a control mechanism in which the toothed wheel is secured to an xe2x80x9cengagementxe2x80x9d first shaft which is coupled to the moving contact via a xe2x80x9cmainxe2x80x9d second shaft, as generally applies in latest-generation control mechanisms for high-voltage circuit-breakers.
It should be noted that, independently of whether or not the control mechanism has a single shaft, the coupling between the shaft(s) and a moving contact of the circuit-breaker is not reversible, i.e. the engagement spring may be re-tensioned by turning the cog wheel after the circuit-breaker has closed without causing said circuit-breaker to open. The cog wheel is driven by an electric motor to re-load the control mechanism, and the toothed wheel turns in the same direction when the engagement spring relaxes, and when it is re-tensioned by the motor.
The term xe2x80x9cspringxe2x80x9d is generally used below to designate the engagement spring which is connected to the toothed wheel and which is suitable for driving it.
At the end of re-loading of the spring, the toothed wheel is stopped from turning when said toothed wheel reaches the first angular position which corresponds substantially to the spring tension being at its maximum. A pawl is generally disposed facing a cam constrained to move with the toothed wheel so that the cam comes into abutment against said pawl when the toothed wheel reaches the first angular position. The pawl is generally hinged so that, by being disengaged, it releases the toothed wheel and triggers closure of the circuit-breaker by means of the spring relaxing.
Stopping the motor by interrupting its electrical power supply is not suitable for bringing the toothed wheel to a stop with sufficient accuracy, because the inertia of the motor delays such a stop. Such a control mechanism thus generally further comprises a mechanical device for decoupling the motor from the toothed wheel when it reaches its first angular position. Without such a device, the forces generated by the inertia of the motor in the teeth and in the pawl would give rise to considerable wear of the control mechanism, which would rapidly lead to its destruction.
Patent Document EP 0 917 168 discloses a large number of component elements which can be used in a mechanical control mechanism of the invention. The toothed wheel includes a plurality of teeth that can slide towards the inside of the toothed wheel, those sliding teeth being situated in a zone of the toothed wheel that corresponds to the position of the cog wheel when the toothed wheel is in the first angular position. Each sliding tooth is suitable for retracting by sliding radially against a return spring which is specific to it. More particularly, each sliding tooth has an asymmetrical profile with a tooth head forming a sloping surface, so that, when they mesh with the cog wheel, the sliding teeth retract under the thrust force to which they are subjected from the cog wheel, thereby mechanically decoupling the motor from the toothed wheel. Those sliding teeth are spaced apart at a distance significantly larger than the pitch of the teeth on the remainder of the toothed wheel, so as to facilitate re-meshing with the cog wheel when the spring relaxes.
Such a configuration requires a sliding system for each tooth, which represents significant extra machining and manufacturing cost. Furthermore, the retractable teeth have a special profile, each of them including a tooth head in the form of a sloping surface, which further increases the manufacturing cost.
A control mechanism is known from patent document JP 01154418, said control mechanism comprising a cog wheel and a toothed wheel having a peripheral set of teeth that included a toothed segment that is retractable. The segment comprises two teeth spaced apart from each other at a distance corresponding substantially to twice the regular pitch of the primary set of teeth. When the segment is in its deployed position, each of its two teeth is at the same distance from the closest tooth to the primary set of teeth.
However, as explained in the preamble of patent document U.S. Pat. No. 5,723,836, this configuration is not satisfactory. In that document, it is stated that decoupling the cog wheel and the toothed wheel implies oscillation of the retractable segment such that collisions between the teeth of the cog wheel and the tooth at the oscillating end of the segment risk causing surface damage to at least one tooth. Consequently, rigorous examination of the surface state of the teeth is necessary in order to limit the risk of such damage, thereby leading to an increase in the manufacturing cost of the control mechanism.
While retaining the principle of a circuit-breaker control mechanism in which the teeth of the toothed wheel include teeth disposed on a retractable segment, an object of the invention is to remedy the drawbacks of the state of the art by providing a system that is more reliable, for a lower manufacturing cost.
To this end, the invention provides a spring-loaded mechanical control mechanism for a circuit-breaker in a high-voltage or medium-voltage grid, said control mechanism comprising a toothed wheel turned by a spring from a first angular position to a second angular position, and a cog wheel co-operating with the toothed wheel to displace it from the second angular position to the first angular position so as to tension said spring, said toothed wheel having a peripheral set of teeth constituted firstly by a primary set of teeth secured to the wheel, and secondly by a portion of a set of teeth in the form of a retractable toothed segment, said primary set of teeth having constant pitch, wherein said retractable segment comprises at least four teeth spaced apart from one another at the same constant pitch as the pitch of said primary teeth.
The retractable segment thus has a conventional set of teeth which requires no special machining, which further reduces the manufacturing cost of the control mechanism of the invention.
In a preferred embodiment of the invention, the segment is hinged in said toothed wheel via a first end, while being retained by a return spring urging it outwards into a deployed position. The return spring can advantageously be constituted by a V-shaped blade. The segment retracts naturally when it meshes with the cog wheel at the first end, so that it is not necessary to provide any mechanism for controlling the position of the retractable segment, which simplifies the control mechanism of the invention.
In another particular embodiment of the invention, the hinge is situated within a circle whose diameter is the same as the base diameter of the set of teeth of said toothed wheel. With this configuration, the cog wheel is decoupled from the wheel at the end of re-loading of the engagement spring, but it re-couples spontaneously with the toothed wheel when the return spring relaxes, even if the segment remains in a retracted position after the motor has stopped completely.
Advantageously, the hinge of the segment comprises a pin which is positioned at a distance from the base diameter lying in the range one to two times the distance between the base diameter and the pitch diameter. This disposition, which allows substantially tangential movement in addition to the generally radial movement of the teeth of the retractable segment, allows anticipated meshing of the cog wheel in the teeth of the retractable segment so as to further decrease the pressing forces between the teeth of the cog wheel and of the segment, and thereby improve the life time of the control mechanism of the invention.
In yet another particular embodiment of the invention, the segment retracts into the thickness of the toothed wheel between two plates forming side plates of the toothed wheel. Thus, the toothed wheel is compact, and the set of teeth can be formed by cutting the plates.